In a wireless cellular communications system, a receiving end generally can demodulate a received signal to obtain data contained in the signal only after learning a channel from a transmitting end to the receiving end (referred to as channel estimation). A common practice is that the transmitting end sends to the receiving end a group of symbols (referred to as reference signals in a Long Term Evolution (LTE) standard known to the transmitting end and the receiving end, and the receiving end performs channel estimation according to the received reference signals. In an LTE system, a group of reference signals distributed on a specific time and a frequency resource (time-frequency resource) is referred to as an antenna port. A base station maps the antenna port to a physical antenna when transmitting data, where the data is generally placed on a time-frequency resource that is not occupied by a reference signal. The receiving end can, once learning a channel at a reference signal position, obtain a channel corresponding to a data position on the antenna port according to a correlation in time and frequency between wireless channels, so as to acquire the data therefrom. The LTE system differentiates antenna ports by numbering them uniformly, for example, an antenna port 0, an antenna port 1, an antenna port 2, an antenna port 3, and the like.
A heterogeneous network, which is a common network in a wireless cellular communications system, refers to a network that does not have a same transmission media and communications protocol. A common networking mode of heterogeneous networks is deploying several micro base stations within a coverage scope of a macro base station. These micro base stations are generally low-power nodes (LPNs), where a transmit power thereof is much less than the macro base station. An antenna configuration of the macro antenna and of each LPN may be different from each other. In order to avoid a problem of inter-cell interference and a handover that is caused when the macro base station and the LPNs are configured as different cells, the macro base station and the LPNs are generally configured as a same cell. However, because the number of antennas between the macro base station and the LPNs, and between the LPNs may be different, how to implement mapping between an antenna port and a physical antenna becomes a problem to be solved for implementing transmit diversity in the foregoing scenario.
The LTE system has the following technical solution:
All antennas on the macro base station and the LPNs are configured as an antenna port 0, that is, configured as a control channel, including a physical broadcast channel (PBCH), a physical control format indicator channel (PCFICH,), a physical downlink control channel (PDCCH1), and a physical hybrid ARQ indicator channel (PHICH), and a cell-specific reference signal (CRS) occupy only the antenna port 0. This solution deems that a cell has only one transmit antenna when transmitting a control channel and a CRS, regardless of the number of antennas on the macro base station and the LPNs. The foregoing solution has the following shortcomings: if the macro base station or an LPN has multiple antennas but the solution regards them as one antenna, no diversity gain can be obtained by using transmit diversity of the multiple antennas; regarding multiple antennas as one antenna is equivalent to using an all-ones precoding codebook, where a cavity position may be formed at different spatial positions (i.e. a value of the channel attenuates greatly at a certain position in space under the impact of the channel after codebooks are superposed, resulting in very poor performance of a receiver at such a position, and a failure in implementing a universal coverage).